References of "Ottersten, Björn 50002797"
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See detailFeasibility study of full-duplex relaying in satellite networks
Bhavani Shankar, M. R.; Zheng, G.; Maleki, Sina UL et al

in IEEE Workshop on Signal Processing Advances in Wireless Communications, SPAWC (2015), 2015-August

With the successful implementation of full-duplex radio prototypes, traditional orthogonal half-duplex communications is deemed to be inefficient in certain terrestrial applications. While full-duplex ... [more ▼]

With the successful implementation of full-duplex radio prototypes, traditional orthogonal half-duplex communications is deemed to be inefficient in certain terrestrial applications. While full-duplex techniques are gaining interest in terrestrial communications, thanks to the trend of short-distance and low-power transmissions, their application to satellite communications has drawn little attention. Motivated by this, the paper explores the use of the full-duplex relaying operation on-board the satellite in a DVB-S2 compliant network. Self-interference, whose management is the key component of a full-duplex communication, is the focus of study in this paper. Modelling the effects of self-interference and power amplifier nonlinearities on the quality of the received signal in undertaken. Subsequently, closed-form expressions for the various interference components are derived. The numerical evaluations of derived expressions rely on realistic link budgets and indicate substantial gains in spectral efficiency when self-interference can be well calibrated and measured. This confirms that the satellite full-duplex communications could be a promising solution for the efficient use of satellite spectrum, at least from a technical point of view. © 2015 IEEE. [less ▲]

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See detailMultiple-input multiple-output symbol rate signal digital predistorter for non-linear multi-carrier satellite channels
Zenteno, Efrain; Piazza, Roberto; Bhavani Shankar, M. R. et al

in Communications, IET (2015), 9(16), 2053--2059

A digital predistortion (DPD) scheme is presented for non-linear distortion mitigation in multi-carrier satellite communication channels. The proposed DPD has a multiple-input multiple-output architecture ... [more ▼]

A digital predistortion (DPD) scheme is presented for non-linear distortion mitigation in multi-carrier satellite communication channels. The proposed DPD has a multiple-input multiple-output architecture similar to data DPD schemes. However, it enhances the mitigation performance of data DPDs using a multi-rate processing algorithm to achieve spectrum broadening of non-linear operators. Compared to single carrier (single-input single-output) signal (waveform) DPD schemes, the proposed DPD has lower digital processing rate reducing the required hardware cost of the predistorter. The proposed DPD outperforms, in total degradation, both data and signal DPD schemes. Further, it performs closest to a channel bound described by an ideally mitigated channel with limited maximum output power. © 2015. The Institution of Engineering and Technology. [less ▲]

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See detailMaximizing energy efficiency in multiple access channels by exploiting packet dropping and transmitter buffering
Butt, M. M.; Jorswieck, E. A.; Ottersten, Björn UL

in IEEE Transactions on Wireless Communications (2015), 14(8), 4129-4141

Quality of service (QoS) for a network is characterized in terms of various parameters specifying packet delay and loss tolerance requirements for the application. The unpredictable nature of the wireless ... [more ▼]

Quality of service (QoS) for a network is characterized in terms of various parameters specifying packet delay and loss tolerance requirements for the application. The unpredictable nature of the wireless channel demands for application of certain mechanisms to meet the QoS requirements. Traditionally, medium access control (MAC) and network layers perform these tasks. However, these mechanisms do not take (fading) channel conditions into account. In this paper, we investigate the problem using cross layer techniques where information flow and joint optimization of higher and physical layer is permitted. We propose a scheduling scheme to optimize the energy consumption of a multiuser multi-access system such that QoS constraints in terms of packet loss are fulfilled while the system is able to maximize the advantages emerging from multiuser diversity. Specifically, this work focuses on modeling and analyzing the effects of packet buffering capabilities of the transmitter on the system energy for a packet loss tolerant application. We discuss low complexity schemes which show comparable performance to the proposed scheme. The numerical evaluation reveals useful insights about the coupling effects of different QoS parameters on the system energy consumption and validates our analytical results. © 2002-2012 IEEE. [less ▲]

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See detailUser Scheduling in Cooperative Satellite Systems
Christopoulos, Dimitrios UL; Chatzinotas, Symeon UL; Ottersten, Björn UL

in Cooperative and Cognitive Satellite Systems (2015)

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See detailMultiple Gateway Transmit Diversity in Q/V Band Feeder Links
Gharanjik, Ahmad UL; Shankar, Bhavani UL; Arapoglou, Pantelis-Daniel et al

in IEEE Transactions on Communications (2015)

Design of high bandwidth and reliable feeder links is central towards provisioning new services on the user link of a multibeam satellite communication (SatCom) system. Towards this, utilization of the Q ... [more ▼]

Design of high bandwidth and reliable feeder links is central towards provisioning new services on the user link of a multibeam satellite communication (SatCom) system. Towards this, utilization of the Q/V band and an exploitation of multiple gateways (GW) as a transmit diversity measure for overcoming severe propagation effects are being considered. In this context, this contribution deals with the design of a feeder link comprising N + P GWs (N active and P redundant GWs). Towards provisioning the desired availability, a novel switching scheme is analysed and practical aspects such as prediction based switching and switching rate are discussed. Unlike most relevant works, a dynamic rain attenuation model is used to derive analytically average outage probability in the fundamental 1 + 1 gateway case. Building on this result, an analysis for the N +P scenario leading to a quantification of the end􀀀to􀀀end performance is provided. This analysis aids system sizing by illustrating the interplay between the number of active and redundant gateways on the chosen metrics : average outage and average switching rate. [less ▲]

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See detailEnergy Efficient Coordinated Beamforming for Multicell System: Duality-Based Algorithm Design and Massive MIMO Transition
He, Shiwen; Huang, Yongming; Yang, Luxi et al

in IEEE TRANSACTIONS ON COMMUNICATIONS (2015), 63(12), 4920-4935

In this paper, we investigate joint beamforming and power allocation in multicell multiple-input single-output (MISO) downlink networks. Our goal is to maximize the utility function defined as the ratio ... [more ▼]

In this paper, we investigate joint beamforming and power allocation in multicell multiple-input single-output (MISO) downlink networks. Our goal is to maximize the utility function defined as the ratio between the system weighted sum rate and the total power consumption subject to the users' quality of service requirements and per-base-station (BS) power constraints. The considered problem is nonconvex and its objective is in a fractional form. To circumvent this problem, we first resort to an virtual uplink formulations of the the primal problem by introducing an auxiliary variable and applying the uplink-downlink duality theory. By exploiting the analytic structure of the optimal beamformers in the dual uplink problem, an efficient algorithm is then developed to solve the considered problem. Furthermore, to reduce further the exchange overhead between coordinated BSs in a large-scale antenna system, an effective coordinated power allocation solution only based on statistical channel state information is reached by deriving the asymptotic optimization problem, which is used to obtain the power allocation in a long-term timescale. Numerical results validate the effectiveness of our proposed schemes and show that both the spectral efficiency and the energy efficiency can be simultaneously improved over traditional downlink coordinated schemes, especially in the middle-high transmit power region. [less ▲]

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See detailView-Independent Enhanced 3D Reconstruction of Non-Rigidly Deforming Objects
Afzal, Hassan UL; Aouada, Djamila UL; Destelle, Francois et al

in 16th International Conference on Computer Analysis of Images and Patterns (2015)

In this paper, we target enhanced 3D reconstruction of non-rigidly deforming objects based on a view-independent surface representation with an automated recursive filtering scheme. This work improves ... [more ▼]

In this paper, we target enhanced 3D reconstruction of non-rigidly deforming objects based on a view-independent surface representation with an automated recursive filtering scheme. This work improves upon the KinectDeform algorithm which we recently proposed. KinectDeform uses an implicit viewdependent volumetric truncated signed distance function (TSDF) based surface representation. The view-dependence makes its pipeline complex by requiring surface prediction and extraction steps based on camera’s field of view. This paper proposes to use an explicit projection-based Moving Least Squares (MLS) surface representation from point-sets. Moreover, the empirical weighted filtering scheme in KinectDeform is replaced by an automated fusion scheme based on a Kalman filter. We analyze the performance of the proposed algorithm both qualitatively and quantitatively and show that it is able to produce enhanced and feature preserving 3D reconstructions. [less ▲]

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See detailGeneralized direct predistortion with adaptive crest factor reduction control
Piazza, Roberto UL; Bhavani Shankar, M. R.; Ottersten, Björn UL

in Proceedings of ICASSP, IEEE International Conference on Acoustics, Speech and Signal Processing (2015), 2015-August

Efficient power amplification is inherently a non linear operation that introduces unwanted interference in the amplified signal. Strong inter-symbol interference is generated when the amplifier non ... [more ▼]

Efficient power amplification is inherently a non linear operation that introduces unwanted interference in the amplified signal. Strong inter-symbol interference is generated when the amplifier non linearity is combined with channel memory effects. Further, signals with very high peak to average power ratio, typical of multiple carrier systems, are even more sensitive to the non linearities resulting in severe distortion effects. Signal pre-clipping (crest factor reduction) and predistortion are conventional countermeasure techniques to reduce the generated non linear distortion and improve power and spectral efficiency. In this work, novel optimization methods for predistortion and pre-clipping are analytically derived for a general non-linear communication channel with memory. A combined architecture in which crest factor reduction is followed by signal predistortion is proposed and the parameters are estimated resorting to iterative algorithms based on least squares method. Performance evaluation of the estimation techniques shows the effectiveness of the derived algorithms and significant gain compared to previously known methods. © 2015 IEEE. [less ▲]

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See detailCellular-broadcast service convergence through caching for CoMP cloud RANs
Chatzinotas, Symeon UL; Christopoulos, Dimitrios; Ottersten, Björn UL

in arXiv preprint arXiv:1504.08274 (2015)

Cellular and Broadcast services have been traditionally treated independently due to the different market requirements, thus resulting in different business models and orthogonal frequency allocations ... [more ▼]

Cellular and Broadcast services have been traditionally treated independently due to the different market requirements, thus resulting in different business models and orthogonal frequency allocations. However, with the advent of cheap memory and smart caching, this traditional paradigm can converge into a single system which can provide both services in an efficient manner. This paper focuses on multimedia delivery through an integrated network, including both a cellular (also known as unicast or broadband) and a broadcast last mile operating over shared spectrum. The subscribers of the network are equipped with a cache which can effectively create zero perceived latency for multimedia delivery, assuming that the content has been proactively and intelligently cached. The main objective of this work is to establish analytically the optimal content popularity threshold, based on a intuitive cost function. In other words, the aim is to derive which content should be broadcasted and which content should be unicasted. To facilitate this, Cooperative Multi- Point (CoMP) joint processing algorithms are employed for the uni and broad-cast PHY transmissions. To practically implement this, the integrated network controller is assumed to have access to traffic statistics in terms of content popularity. Simulation results are provided to assess the gain in terms of total spectral efficiency. A conventional system, where the two networks operate independently, is used as benchmark. [less ▲]

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See detailPerformance Analysis of Noncoherent Frame Synchronization in Satellite Communications with Frequency Uncertainty
Mazzali, Nicolò UL; Stante, Giulio; Shankar, Bhavani UL et al

in Proceedings on IEEE Symposium on Communications and Vehicular Technology in the Benelux (2015)

Emerging markets for satellite communications, such as maritime and aeronautical applications, require reliable communications in challenging conditions and low-cost, low-complexity user terminals. In ... [more ▼]

Emerging markets for satellite communications, such as maritime and aeronautical applications, require reliable communications in challenging conditions and low-cost, low-complexity user terminals. In this perspective, the synchronization chain is a fundamental part of the receiver and its design becomes critical. When a quadricorrelator is used as first stage of the synchronization chain so as to perform a coarse frequency estimation, then a noncoherent algorithm for frame synchronization can be employed as second stage. A popular algorithm for frame synchronization is the post-detection integration (PDI), whose noncoherent version (NCPDI) is quite robust to non-negligible residual frequency offsets. In this paper we will assess the performance of NCPDI in presence of a random uniformly-distributed residual frequency offset and will find a closed-form approximation for the probability of detection. Moreover, we will optimize the design parameters of NCPDI for a system operating at very low signal-to-noise ratio (VL-SNR) by minimizing the probability of missed detection for a given probability of false alarm. [less ▲]

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See detailResource allocation for cognitive satellite uplink and fixed-service terrestrial coexistence in ka-band
Lagunas, E.; Sharma, Shree Krishna UL; Maleki, Sina UL et al

in Lecture Notes of the Institute for Computer Sciences, Social-Informatics and Telecommunications Engineering, LNICST (2015), 156

This paper addresses the cognitive Geostationary Orbit (GSO) satellite uplink where satellite terminals reuse frequency bands of Fixed-Service (FS) terrestrial microwave links which are the incumbent ... [more ▼]

This paper addresses the cognitive Geostationary Orbit (GSO) satellite uplink where satellite terminals reuse frequency bands of Fixed-Service (FS) terrestrial microwave links which are the incumbent users in the Ka 27.5-29.5 GHz band. In the scenario considered herein, the transmitted power of the cognitive satellite user has to ensure that the interference impact on potentially present FS links does not exceed the regulatory interference limitations. In order to satisfy the interference constraint and assuming the existence of a complete and reliable FS database, this paper proposes a Joint Power and Carrier Allocation (JPCA) strategy to enable the cognitive uplink access to GSO Fixed Satellite Service (FSS) terminals. The proposed approach identifies the worst FS link per user in terms of interference and divides the amount of tolerable interference among the maximum number of FSS terminal users that can potentially interfere with it. In so doing, the cognitive system is guaranteed to never exceed the prescribed interference threshold. Subsequently, powers and carriers are jointly allocated so as to maximize the throughput of the FSS system. Supporting results based on numerical simulations are provided. It is shown that the proposed cognitive approach represents a promising solution to significantly boost the performance of conventional satellite systems. © Institute for Computer Sciences, Social Informatics and Telecommunications Engineering 2015. [less ▲]

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See detailSecrecy Analysis on Network Coding in Bidirectional Multibeam Satellite Communications
Kalantari, Ashkan UL; Ottersten, Björn UL

in IEEE Transactions on Information Forensics and Security (2015)

Network coding is an efficient means to improve the spectrum efficiency of satellite communications. However, its resilience to eavesdropping attacks is not well understood. This paper studies the ... [more ▼]

Network coding is an efficient means to improve the spectrum efficiency of satellite communications. However, its resilience to eavesdropping attacks is not well understood. This paper studies the confidentiality issue in a bidirectional satellite network consisting of two mobile users who want to exchange message via a multibeam satellite using the XOR network coding protocol. We aim to maximize the sum secrecy rate by designing the optimal beamforming vector along with optimizing the return and forward link time allocation. The problem is non-convex, and we find its optimal solution using semidefinite programming together with a 1-D search. For comparison, we also solve the sum secrecy rate maximization problem for a conventional reference scheme without using network coding. Simulation results using realistic system parameters demonstrate that the bidirectional scheme using network coding provides considerably higher secrecy rate compared to that of the conventional scheme. [less ▲]

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See detailFeasibility of Positive Secrecy Rate in Wiretap Interference Channels
Kalantari, Ashkan UL; Maleki, Sina UL; Zheng, Gan et al

in IEEE Global Conference on Signal and Information Processing (GlobalSIP) (2014, December 03)

Interference usually is an adverse phenomenon in wireless networks. However, the interference can potentially be used to boost the secrecy rate in wireless interference channels. This work studies the ... [more ▼]

Interference usually is an adverse phenomenon in wireless networks. However, the interference can potentially be used to boost the secrecy rate in wireless interference channels. This work studies the secrecy rate in a two-user interference network where unintended user may overhear one of the users, namely user 1. User 1 tunes its transmission power in order to maximize its secrecy rate as well as to maintain the quality of service at the other user’s destination, user 2, while both user’s power limits are considered. It is demonstrated that achieving a positive secrecy rate for user 1 only depends on the channel conditions and user 2’s transmission power. Consequently, depending on the channel conditions, the exact threshold for user 2’s transmission power which leads to a positive secrecy rate for user 1 is derived. [less ▲]

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See detailExample-Dependent Cost-Sensitive Logistic Regression for Credit Scoring
Correa Bahnsen, Alejandro UL; Aouada, Djamila UL; Ottersten, Björn UL

in 2014 13th International Conference on Machine Learning and Applications (2014, December 03)

Several real-world classification problems are example-dependent cost-sensitive in nature, where the costs due to misclassification vary between examples. Credit scoring is a typical example of cost ... [more ▼]

Several real-world classification problems are example-dependent cost-sensitive in nature, where the costs due to misclassification vary between examples. Credit scoring is a typical example of cost-sensitive classification. However, it is usually treated using methods that do not take into account the real financial costs associated with the lending business. In this paper, we propose a new example-dependent cost matrix for credit scoring. Furthermore, we propose an algorithm that introduces the example-dependent costs into a logistic regression. Using two publicly available datasets, we compare our proposed method against state-of-the-art example-dependent cost-sensitive algorithms. The results highlight the importance of using real financial costs. Moreover, by using the proposed cost-sensitive logistic regression, significant improvements are made in the sense of higher savings. [less ▲]

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See detailSpatial Multiplexing in Optical Feeder Links for High Throughput Satellites
Gharanjik, Ahmad UL; Liolis, Konstantinos; Shankar, Bhavani UL et al

in Spatial Multiplexing in Optical Feeder Links for High Throughput Satellites (2014, December 02)

Optical feeder links are an attractive alternative to the RF feeder links in satellite communications (SatCom). In this paper, we present initial results from an optical feeder link study. We discuss the ... [more ▼]

Optical feeder links are an attractive alternative to the RF feeder links in satellite communications (SatCom). In this paper, we present initial results from an optical feeder link study. We discuss the architecture of a geostationary earth orbit (GEO) satellite system based on optical feeder links. To mitigate the effects of cloud coverage, which is the main availability-limiting factor, Optical Ground Station (OGS) diversity is employed. Moreover, a spatial multiplexing scheme is considered. Assuming an ON-OFF channel model, the number of required OGSs to ensure availability and throughput requirements is analyzed [less ▲]

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See detailSum Rate Maximizing Multigroup Multicast Beamforming under Per-antenna Power Constraints
Christopoulos, Dimitrios UL; Chatzinotas, Symeon UL; Ottersten, Björn UL

in In Proc. of IEEE, Global Communications Conference, GLOBECOM (2014, December)

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See detailData Predistortion for Multicarrier Satellite Channels Based on Direct Learning
Piazza, Roberto UL; Shankar, Bhavani UL; Ottersten, Björn UL

in IEEE Transactions on Signal Processing (2014), 62(22),

Satellite communication is facing the urgent need of improving data rate and efficiency to compete with the quality of service offered by terrestrial communication systems. An imminent gain, achievable ... [more ▼]

Satellite communication is facing the urgent need of improving data rate and efficiency to compete with the quality of service offered by terrestrial communication systems. An imminent gain, achievable without the need of upgrading current satellite technology, can be obtained by exploiting multicarrier operation at the transponder and using highly efficient modulation schemes. However, on-board multicarrier joint amplification of high order modulation schemes is a critical operation as it brings severe non-linear distortion effects. These distortions increase as the on-board High Power Amplifier (HPA) is operated to yield higher power efficiencies. In this work, we propose novel techniques to implement on ground predistortion that enable multicarrier transmission of highly efficient modulation schemes over satellite channels without impacting infrastructure on the downlink. [less ▲]

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See detailExploiting polarization for spectrum awareness in cognitive satellite communications
Sharma, S. K.; Chatzinotas, Symeon UL; Ottersten, Björn UL

in Exploiting polarization for spectrum awareness in cognitive satellite communications (2014)

The continuously increasing demand of spectrum and current static spectrum allocation policies are rendering the available radio spectrum scarce. To address the problem of spectrum scarcity in the ... [more ▼]

The continuously increasing demand of spectrum and current static spectrum allocation policies are rendering the available radio spectrum scarce. To address the problem of spectrum scarcity in the satellite paradigm, cognitive satellite communications has been considered as a promising technique. In addition to the existing spectrum sharing dimensions such as frequency, time, and space, polarization can be exploited as an additional degree of freedom in order to explore the spectral gaps in the underutilized licensed spectrum. In this context, this chapter firstly provides an overview of the existing works in polarization-based spectrum sharing. Secondly, it presents the theoretical analysis of energy detection technique for dual polarized Additive White Gaussian Noise and Rayleigh fading channels considering the spectral coexistence scenarios of dual and hybrid satellite systems. Thirdly, it provides the comparison of different combining techniques in terms of the sensing performance. Finally, it provides interesting future research directions in this domain. © 2015 by IGI Global. All rights reserved. [less ▲]

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See detailWeighted Fair Multicast Multigroup Beamforming under Per-antenna Power Constraints
Christopoulos, Dimitrios UL; Chatzinotas, Symeon UL; Ottersten, Björn UL

in Signal Processing, IEEE Transactions on (2014), 62(19), 5132-5142

A multi-antenna transmitter that conveys independent sets of common data to distinct groups of users is considered. This model is known as physical layer multicasting to multiple co-channel groups. In ... [more ▼]

A multi-antenna transmitter that conveys independent sets of common data to distinct groups of users is considered. This model is known as physical layer multicasting to multiple co-channel groups. In this context, the practical constraint of a maximum permitted power level radiated by each antenna is addressed. The per-antenna power constrained system is optimized in a maximum fairness sense with respect to predetermined quality of service weights. In other words, the worst scaled user is boosted by maximizing its weighted signal-to-interference plus noise ratio. A detailed solution to tackle the weighted max-min fair multigroup multicast problem under per-antenna power constraints is therefore derived. The implications of the novel constraints are investigated via prominent applications and paradigms. What is more, robust per-antenna constrained multigroup multicast beamforming solutions are proposed. Finally, an extensive performance evaluation quantifies the gains of the proposed algorithm over existing solutions and exhibits its accuracy over per-antenna power constrained systems. [less ▲]

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See detailFrame Based Precoding in Satellite Communications: A Multicast Approach
Christopoulos, Dimitrios UL; Chatzinotas, Symeon UL; Ottersten, Björn UL

in In Proc. of IEEE, Advanced Satellite Multimedia Systems Conference (2014, September)

Detailed reference viewed: 160 (5 UL)